This invention relates to liners and more particularly to liners for warheads.
High powered explosives used in ordnance are sensitive, potentially dangerous materials which must be properly sealed in their containers or warheads. These explosives must be kept out of joints, weld cracks, threads, etc., where they may be pinched and detonated during even normal handling. Further, these explosives must be protected from external chemical attack by water, oils, fuels, and other materials. Moreover, the explosives must be effectively sealed off to prevent the explosives or their ingredients (e.g. plasticizers) from exuding or migrating outside of the warhead or container during long storage or during exposure to extreme environmental conditions. Finally, the explosives should be protected against heat caused by fires or against shocks caused by rough handling.
Commonly the inside surface of the container or warhead casing is lined with a nonenergetic sealer material which serves as a barrier between the explosive and the casing. The liner should be easy to apply and must be compatible with the explosive. The material usually used as a liner for trinitrotoluene based explosives is an asphaltic composition called "hot-melt." However, hot-melt has several disadvantages. First, hot-melt has to be applied at temperatures of from 400.degree. to 500.degree. F; these high temperatures can cause aluminum warheads to distort and can damage internal components and materials such as flexible conduits, wire insulation, potting compounds, and adhesives. Second, hot-melt is a thermoplastic material which can cold-flow or creep under pressure at military environmental temperatures. Exuding hot-melt may clog up electrical connectors, exploder wells, or other mating surfaces. Finally, hot-melt provides poor high temperature protection for the explosive because hot-melt quickly melts when exposed to the high temperatures produced by fires. The explosive can then shift closer to the warhead casing where it is more likely to ignite.
An epoxy/glass-microballoon liner system was used in the MK 46 torpedo warheads. The liner was processed and applied at room temperature, and then dried and cured at a slightly elevated temperature. Unfortunately, this epoxy liner was found to be hard and brittle and cracked very easily; as a result, the epoxy liner did not provide good protection for the explosive. Flexible epoxides are available which do not crack as readily; however, these flexible epoxides are not as effective as the hard epoxides in stopping liquid plasticizers from migrating out of explosives.